Properties of metal bolometers fabricated on porous silicon

Recent studies on thermal properties of porous silicon PS.made possible a new type of structures and processes for a better thermal insulation of chemical and physical sensors. In this work, we propose to use PS as substrate for the sensing element of metal bolometers. PS is obtained by electrochemical anodization of bulk Si in HF-based solutions. By varying HF title and current density during anodization, well defined thin layers with different porosities can be obtained. The sensing elements of the bolometer is a Nb strip, 5 mm wide and 50 nm thick, deposited on PS 40 mm thick. The thermal properties of the strips on PS have been measured both by resistive heating and bolometric method. The results have been compared with those obtained on amorphous glass. Strips on a layer of PS 40 mm thick with a porosity of 60% show a thermal conductance close to that obtained on glass. A responsivity of about 50 V Wy1 and a time constant of 4 ms have been measured for a bolometer deposited on PS with porosity of 60%. q1999 Elsevier Science B.V. All rights reserved.